There are many instances in which the measurement of the dose of radiation, to which either an individual or equipment is exposed, is desirable. This is particularly important for a commander in a nuclear battle field to determine the radiological status of troops. Besides tactical use in a nuclear battle field, there are many commercial applications in which environments of ionizing radiation intensity occur in which an accumulated dose or dose rate need to be detected and accurately indicated. One type of device used to measure radiation dose is a device made from materials with different atomic numbers resulting in a difference in the probability of production of Compton electrons during exposure to gamma rays. This Compton electron emission is used to measure radiation doses. One such device is disclosed in U.S. Pat. No. 4,019,058 entitled "Charge Transport Tactical Dose Meter", issuing to Kronenberg et al on Apr. 19, 1977, which is herein incorporated by reference. Therein disclosed is a quartz fiber electroscope shunted by a variable capacitor and coupled to a radiation detection capacitor. The radiation detection capacitor is formed of a material of relatively large atomic number and a material of lesser atomic number. An electric charge is induced by neutron or gamma radiation. A variable capacitor is then used to determine the voltage as a result of the induced electric charge. The voltage is proportional to the dose.
This type of radiation sensor is called a proton/electron transfer sensor or, hereinafter, PETS. The operation of a PETS dosimeter for detecting gamma rays can be appreciated as follows. A capacitor whose one electrode is made of a higher atomic number conductor than its other electrode and separated by a thin insulator, when exposed to gamma rays, will cause energetic electrons to be generated. The production of photoelectrons per unit mass of the material is proportional to the atomic number to the fifth power. The production of Compton electrons is proportional to the atomic number. Therefore, more electrons will be produced in the higher atomic number electrode than in the lower atomic number electrode. Many electrons will escape from the electrode where they are generated and will be absorbed in other parts of the capacitor. Their range (when expressed in weight per area) does not depend significantly on atomic number and therefore, the higher atomic number electrode will lose more electrons than gaining electrons. This will result in the higher atomic number electrode acquiring a positive charge and the lower atomic number electrode a negative charge. This charge is proportional to the gamma ray dose.
PETS may also be used to measure fast neutrons. A capacitor having one electrode made of a conductive low atomic number hydrogenous material while its other electrode, separated by a hydrogenous insulator, is made of a conductive low atomic number non-hydrogenous material will detect fast neutrons. The atomic numbers of all the involved materials being similar and low. This device will show a very low response to gamma rays. When exposed to fast neutrons, recoil protons will be generated in the hydrogenous electrode and in the insulator. Some of these recoil protons will escape from the hydrogenous electrode charging it negatively and will be absorbed in the non-hydrogenous electrode charging it positively. The amount of accumulated charge will be proportional to the fast neutron dose.
The sensitivity of both types of PETS, for detecting gamma or neutron radiation, will depend on the area of the electrode, the capacitance of the device, and the distance between electrodes. It should be noted that this system is free of any dose rate saturation effects and thus can be used for steady state as well as pulsed radiation application where short pulses delivered at very high rates are encountered.
While the rate of generation of electric charge on the electrodes of a PET is strictly proportional to the radiation dose rate and the electric charge between the two electrodes, which increases linearly with dose, they are not without inaccuracies. There are inaccuracies and adverse effects in PETS as a result of polarization of the dielectric, ionization, and electric charge leakage. Therefore, there is a need for reliable, more accurate dose information to be derived from radiation sensors that operate as a proton/electron transfer sensor or PETS.